Apparatus for removing trip hazards in concrete sidewalks

ABSTRACT

An apparatus for cutting a chamfer on an upper edge of a concrete slab includes a hub designed for installation on the threaded output spindle of an angle grinder, and a specially-modified diamond-grit-edged rotary blade which mounts on the hub. For a preferred embodiment of the hub, an attachment collar is unitary and concentric with both a blade mounting flange having countersunk attachment screw holes and a blade centering shoulder on the flange. The attachment collar has at least one pair of flattened parallel sides for receiving a wrench used to tighten the hub on the output spindle. The blade, which is equipped with both countersunk attachment holes and a central positioning aperture sized to fit closely over the blade centering shoulder, is attachable with countersinking screws to the mounting flange so that the head of each screw is flush with the surface of the blade.

This is a continuation of application Ser. No. 10/975,677, filed on Oct.28, 2004, titled Method and Apparatus for Removing Trip Hazards inConcrete Sidewalks, now U.S. Pat. No. 7,000,606, which was acontinuation of application Ser. No. 10/155,663, filed on May 24, 2002,titled Method and Apparatus for Removing Trip Hazards in ConcreteSidewalks, now U.S. Pat. No. 6,827,074 B2.

BACKGROUND OF THE INVENTION

Signed into law as Section 12181 of Title 42 of the United States Codeon Jul. 26 1990, the Americans with Disabilities Act (ADA) is awide-ranging legislation intended to make American society moreaccessible to people with disabilities. The legislation, which tookeffect on Jul. 26, 1992, mandates, among other things, standards foraccess to public facilities, including public sidewalks. The law notonly requires that curb cuts be made at intersections and crosswalks tofacilitate wheelchair access, but also mandates specifications forslopes and transitions between two surfaces of different levels. Some ofthe relevant provisions of the law are as follows:

-   -   4.5.2 Changes in Level. Changes in level up to ¼ inch (6 mm) may        be vertical and without edge treatment. Changes in level between        ¼ inch and ½ inch (6 mm and 13 mm) shall be beveled with a slope        no greater than 1:2. Changes in level greater than ½ inch        (13 mm) shall be accomplished by means of a ramp that complies        with 4.7 or 4.8.    -   4.72 Slope. Slopes of curb ramps shall comply with 4.8.2.        Transitions from ramps to walks, gutters, or streets shall be        flush and free of abrupt changes. Maximum slopes of adjoining        gutters, road surface immediately adjacent to the curb ramp, or        accessible route shall not exceed 1:20.    -   4.8.2 Slope and Rise. The least possible slope shall be used for        any ramp. The maximum slope of a ramp in new construction shall        be 1:12. The maximum rise for any run shall be 30 inches (760        mm). Curb ramps and ramps to be constructed on existing sites or        in existing building or facilities may have slopes and rises as        allowed in 4.1.6(3)(a) if space limitations prohibit the use of        a 1:12 slope or less.    -   3-a-1. A slope between 1:10 and 1:12 is allowed for a maximum        rise of 6 inches.    -   3-a-1. A slope between 1:8 and 1:10 is allowed for a maximum        rise of 3 inches. A slope steeper than 1:8 is not allowed.

Public sidewalks and private sidewalks open to the public must complywith the foregoing provisions of the ADA. Tree roots are the single mostsignificant cause of unlevel conditions of sidewalks. Because sidewalksare generally made of contiguous concrete slabs, unevenness typicallyoccurs at the joints between the slabs. Unstable and inadequatelycompacted soils can also lead to differential settling of adjacentslabs.

Historically, trip hazards caused by uneven lifting and settling ofcontiguous sidewalk sections have been eliminated either by tearing outthe old concrete and replacing it with new slabs having no abrupttransitions between joints, by forming a transition ramp on thelowermost section with macadam, or by creating a chamfer on the edge ofthe uppermost section. The first method represents the most expensivefix. The second method, which uses dark-colored macadam on alight-colored sidewalk, is unsightly. If the chamfer is made using asurface cutter or grinder, the second method is slow, given that allmaterial removed through grinding must be pulverized. In addition, ifthe process is performed with a drum cutter, the equipment is relativelyexpensive and leaves a rough surface. In addition, most equipment usedheretofore is incapable of removing the trip hazard over the entirewidth of a sidewalk. Furthermore, if two adjacent sidewalk slabs havetwisted in opposite directions as they have settled or raised, it may benecessary to create a ramp across a portion of the width of the sidewalkon both sides of the joint.

What is needed is a new method and apparatus that will reduce the timerequired to form chamfers, that is capable of removing a trip hazardover the entire width of a sidewalk, and that is capable of chamferingportions of two intersecting slabs at a common joint. Ideally, theequipment and expendables required will be relatively simple andinexpensive, and will not require pulverization of all material removedduring a chamfer operation.

SUMMARY OF THE INVENTION

The present invention provides both a method and apparatus for cutting achamfer on an upper edge of a concrete slab. First and second embodimentapparatuses include a hub having a threaded aperture designed forinstallation on the threaded output spindle of an angle grinder, and aspecially-modified diamond-grit-edged rotary blade which mounts on thehub. For a presently preferred embodiment of the hub, an attachmentcollar is unitary and concentric with both a blade mounting flange and ablade centering shoulder on the flange. The attachment collar ismachined for a minimum clearance, self-centering fit on the outputspindle to minimize imbalance conditions. The collar has at least onepair of flattened parallel sides for receiving a wrench used to tightenthe hub on the output spindle. The side of the blade mounting flangeopposite the collar is equipped with at least two, and preferably threeor more, countersunk holes, by means of which the blade may be attached.The holes may be blind, or may penetrate the flange. In the former case,the holes are threaded. In the latter case, the holes are unthreaded andthe screws are secured with self-locking nuts on the side of the collarside of the blade mounting flange. The rotary blade is equipped with acentral positioning aperture sized to fit over the blade centeringshoulder with a generally minimum amount of clearance required for anon-interference fit. The blade is equipped with countersunk holes whichalign with those on the blade mounting flange. Countersinking screws areemployed to affix the blade to the blade mounting flange. When fullytightened in the countersunk holes in the flange, the head of each ofthe screws is flush with the surface of the blade. As the blade rotatesand cuts into concrete, the lower surface of the blade may remain incontact with the lower cut surface. Because the hub will contact theconcrete above the cut, that concrete must be periodically broken andremoved to provide adequate clearance for the hub as the cut iscontinued.

Third and fourth embodiment apparatuses employ a hub having a centralaperture machined for close tolerance mounting on the output spindle ofthe right-angle grinder. The blade has a core with a central recess. Anut, which engages the end of the output spindle, secures the blade tothe hub and spindle. The nut may be separate from the blade assembly, inwhich case, the hub incorporates a blade centering shoulder which mateswith a central positioning aperture in the blade core. Alternatively,the nut may be incorporated in the blade assembly. For example, the nutmay be swedged within a central blade aperture. As will be hereinaftershown, certain modifications are made to the hub to accommodate theswedged nut.

With training, a skilled worker can make an angled chamfer cut into theedge of a raised concrete slab, so that a smooth transition between alower slab and the raised slab may be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawing FIGS. 1-10 show a first embodiment apparatus; FIGS. 11-14, asecond embodiment apparatus; FIG. 14, a blade guard; FIGS. 16-21, athird embodiment apparatus; and FIGS. 22-24 a fourth embodimentapparatus.

FIG. 1 is a side elevational view of a typical electric right-anglegrinder;

FIG. 2 is a top plan view of a first embodiment hub;

FIG. 3 is side elevational view of the first embodiment hub, takenparallel to the wrench flats;

FIG. 4 is side-elevational see-through view of the first embodiment hub,taken perpendicular to the wrench flats;

FIG. 5 is an isometric top view of the first embodiment hub;

FIG. 6 is an isometric bottom view of the first embodiment hub;

FIG. 7 is a top plan view of the blade;

FIG. 8 is an exploded side elevational view of the right-angled grinderof FIG. 1, the hub of FIGS. 2-6, the blade of FIG. 7, and multiplecountersinking screws, positioned for assembly;

FIG. 9 is a side elevational view of the right-angled grinder of FIG. 1,having installed thereon the hub of FIGS. 2-6 and the blade of FIG. 7;

FIG. 10 is an enlarged cross-sectional view of the portion of FIG. 9within the ellipse 10, taken through the central axis and a pair ofblade-securing holes;

FIG. 11 is an isometric top view of a second embodiment hub having blindholes for blade retaining screws;

FIG. 12 is an isometric top view of the second embodiment hub;

FIG. 13 is an exploded side elevational view of a portion of theright-angled grinder of FIG. 1, the hub of FIGS. 12-13, the blade ofFIG. 7, and multiple countersinking screws, positioned for assembly;

FIG. 14 an enlarged cross-sectional view of a portion of the assembledcomponents of FIG. 13, the view being comparable to that of FIG. 10;

FIG. 15 is a side elevational view of the right-angled grinder of FIG.1, having installed thereon the hub of FIGS. 2-6, the blade of FIG. 7,and a blade guard trimmed to function with the blade and hub of thepresent invention;

FIG. 16 is an isometric top view of a third embodiment hub having anunthreaded central aperture;

FIG. 17 is an isometric top view of the third embodiment hub;

FIG. 18 is an exploded side elevational view of a portion of theright-angled grinder of FIG. 1, the hub of FIGS. 16-17, a speciallydesigned blade having a core with a concave center region, and aretaining nut, all positioned for assembly;

FIG. 19 is an isometric view of the retaining nut first shown in FIG.18;

FIG. 20 is a cross-sectional view of the assembled components of FIG.18;

FIG. 21 is an isometric top view of a fourth embodiment hub having anunthreaded central aperture;

FIG. 22 is an isometric top view of the fourth embodiment hub;

FIG. 23 is an exploded side elevational view of a portion of theright-angled grinder of FIG. 1, the hub of FIGS. 21-22, a speciallydesigned blade having a core with a concave center region, and anintegral swedged retaining nut, all positioned for assembly;

FIG. 24 is a cross-sectional view of the assembled components of FIG.23;

FIG. 25 is a side elevational view of the mounted blade making a firstchamfer cut on the edge of a raised concrete slab;

FIG. 26 is a side elevational view of the concrete slab, with thecutting equipment removed following the first cutting pass;

FIG. 27 is a side elevational view of the cut concrete slab of FIG. 26,following the fracturing of the first overhanging ledge;

FIG. 28 is a side elevational view of the mounted blade making a secondchamfer cut on the edge of the raised concrete slab shown in FIG. 25;

FIG. 29 is a side elevational view of the concrete slab, with thecutting equipment removed following the second cutting pass;

FIG. 30 is a side elevational view of the cut concrete slab of FIG. 29,following the fracturing of the second overhanging ledge;

FIG. 31 is a side elevational view of the mounted blade making a thirdchamfer cut on the edge of the raised concrete slab shown in FIG. 25;and

FIG. 32 is the concrete slab shown in FIG. 25 following completion ofthe chamfer cut, and removal of the cutting equipment and debris.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of an apparatus for cutting a chamfer on an upperedge of a concrete slab will now be described with reference to drawingFIGS. 1 through 24. Description of a method for cutting the chamfer willreference drawing FIGS. 25-32.

Referring now to FIG. 1, a typical right-angle grinder motor 100 isshown. The grinder motor 100 has a body 101, which encloses an electricdrive motor, a cooling fan and a right-angle gear train (none of whichare visible in this drawing). The grinder motor 100 has a rotatablypowered threaded output spindle 102, a handle 103, a power switch 104,motor brush caps 105, cooling vents 106, and an electrical power cord107. Although the invention will be shown in combination with anelectrically-powered right-angle grinder, it will be obvious to those ofordinary skill in the art of grinding equipment that acompressed-air-powered right-angle grinder may be used in combinationwith the invention with equally satisfactory results.

Referring now to FIGS. 2 through 6, the apparatus of the inventioncomprises a hub 200 at is designed for installation on the threadedoutput spindle 102 of an angle grinder, such as the electric grindermotor 100 shown in FIG. 1. For a first and preferred embodiment of thehub 200, an attachment collar 201 is unitary and concentric with both ablade mounting flange 202 and a blade centering shoulder 203 on theflange 202. A central mounting aperture 204 passes through the collar201, the flange 202, and the shoulder 203. The mounting aperture 204 isthreaded to receive and engage the threaded output spindle 102 of theright-angle grinder motor 100. The attachment collar 201 has at leastone pair of flattened parallel sides 205 for receiving a wrench used totighten the hub 200 on the output spindle 102. The side 206 of the blademounting flange 202 opposite the collar 201 is equipped with at leasttwo, and preferably three or more, countersunk holes 207, by means ofwhich a generally circular, diamond-grit-edged rotary blade may beattached with countersinking screws and self-locking nuts (not shown inthis drawing figure).

Referring now to FIG. 7, the rotary blade 700 is equipped with a centralpositioning aperture 701 sized to fit over the blade centering shoulder203 with a generally minimum amount of clearance required for anon-interference fit. The blade is equipped with non-threadedcountersunk holes 702 which align with the threaded countersunk holes202 on the blade mounting flange 202. Countersinking screws (shown inFIG. 8) are employed to affix the blade 700 to the blade mounting flange202. When fully tightened in the countersunk threaded holes 202 in theflange 202, the heads of each of the screws is flush with the surface ofthe blade 700. Although it is possible to countersink only the holes 702of the saw blade 700 and use specially designed screws having a veryshallow countersinking head, conventional countersinking screws havegreater structural integrity. The edge 703 of blade 700 is formed from ametal matrix which incorporates diamond grit throughout, which enablesthe blade, when rotating, to cut through “green” or seasoned concrete.For a presently preferred embodiment of the blade, the new diameter is 8inches (about 203 mm), and the blade core has a thickness of about 0.55inch. The height of the blade centering shoulder 203 is preferably alsoabout 0.055 inch. If the blade centering shoulder were to protrudethrough the blade, the edges thereof would become peened over the edgesof the blade centering aperture 701, thereby making removal of the bladedifficult.

Referring now to the exploded assembly 800 of FIG. 8, anelectrically-powered right-angle grinder motor 100 is shown togetherwith the hub 200, the blade 700, multiple countersinkingblade-attachment screws 801 and multiple self-locking nuts 802, allpositioned for assembly as a unit. It will be noted that each of theself-locking nuts has a deformable polymeric insert 1005, which providesthe self-locking function.

Referring now to assembled unit 900 of FIG. 9, the hub 200 has beeninstalled on the output spindle 102 of the right-angled grinder motor100, and the blade 700 has been secured to the hub 200 with thecountersinking screws 801 and the self-locking nuts 802. It will benoted that the lower surface 901 of the blade 700 is completely flat,with no attachment hardware protruding below its surface.

Referring now to FIG. 10, the portion of FIG. 9 within the ellipse 10 isshown in cross-sectional format. In this detailed view, it is clearlyseen that the attachment collar 201 is unitary and concentric with theblade mounting flange 202 and the blade centering shoulder 203 on theflange 202. The threads 1001 within the central mounting aperture 204,which have spirally engaged the threads 1002 on the output spindle 102,are clearly visible in this view. It will be noted that the head 1003 ofeach countersinking blade attachment screw 801 has a socket 1004. Theblade attachment screws 801 are inserted through the countersunk holes702 in the blade 700, through the holes 207 in the blade mounting flange202 and secured with the self-locking nuts 802. Using an allen-typewrench which engages the sockets 1004, the screws 801 may be kept fromrotating while the self-locking nuts 802 are tightened against the uppersurface of the blade mounting flange 202, thereby securing the blade 700to the hub 200. It will also be noted that the central positioningaperture 701 in the blade 700 is sized to fit over the blade centeringshoulder 203 with a generally minimum amount of clearance required for anon-interference fit.

Referring now to FIGS. 11 through 14, a second embodiment of the hub1100 is shown. Identical numbers are used for identical items of thefirst and second embodiments. The only difference between the firstembodiment hub 200 and the second embodiment hub 1100 is that the latterhas countersunk and threaded blade attachment holes 1201 in place of theself-locking nuts 802. Shorter screws 1301 may therefore be employedwith this arrangement. It has been determined that the dust from thecutting process tends to cause the blade attachment screws 1301 to seizewithin the threaded holes, making it difficult to remove a blade 700when it must be replaced. This problem may be solved by using blueLoctite® thread-locking and anti-seizing compound, or a similar product,when installing the blade. The thread-locking and anti-seizing compoundseals the threads on both the screws 1301 and within the bladeattachment holes 1201 from dust.

It should be mentioned that right-angle grinders are sold with a guardthat shields the rear half of a grinding wheel. As grinding wheels areof generally greater thickness than a concrete cutting blade, the guardmust be trimmed so that it does not extend beyond the lower surface ofthe concrete cutting blade. In this way, flush cuts are possible, evenwith the blade guard installed on the grinder motor. Referring now toFIG. 15, a guard 1501 is shown. The guard has been trimmed along thelower edge thereof so that it does not extend below the lower surface ofthe concrete cutting blade 700 when it is mounted on the hub 200, whichis installed on the threaded output spindle 102 of the right-anglegrinder 100.

Referring now to FIGS. 16 and 17, a third embodiment hub 1600 has anaxis of rotation 1601, a central aperture 1602 coincident with the axisof rotation 1601, the aperture sized for close tolerance mounting on theoutput spindle 102 of the right-angle grinder 100, thereby minimizingrotational imbalances. It will be noted that the lower surface 1603 ofthe hub 1600 is recessed, and that the recessed lower surface 1603incorporates a blade centering shoulder 203. The recessed lower surface1603 acts as a backing surface to which the blade is mated.

Referring now to FIG. 18, a generally circular blade 1800 has an axis ofrotation 1801, a generally laminar metal core 1802, and a metal matrixedge 703 affixed to a circumferential edge of the core 1802, the metalmatrix edge being embedded with diamond grit. The laminar metal core1802, which is preferably stamped from sheet steel, includes a centerportion 1803 with a raised upper surface 1804 and an indented lowersurface 1805, said core having a planar flange portion 1806 extendingradially from the center portion 1803, said flange portion having anouter circular circumferential edge 1807, to which metal matrix edge 703is affixed. At the very center of the center portion 1803 is a centralmounting hole 1808 sized to snugly fit over the blade centering shoulder203 of the hub 1600. When the blade 1800 is mounted to the hub, at leasta portion of the raised upper surface 1804 mates with the lower surface1603 of the hub 1600. Also shown in this exploded view is a nut 1900,which engages the threads on the end of the output spindle 102. The nut1900 may be employed to secure the blade 1800 and the hub 1600 to theoutput spindle 102. For a preferred embodiment of the blade, the centerportion 1803 of the core 1802 is bell shaped, having a circular centraldisk portion 1809, which incorporates the central mounting hole 1808,the central disk portion 1809 being coupled to a conical-shaped skirtportion 1810 that is, in turn, coupled to the flange portion 1806. Forthis particular embodiment of the blade 1800, the nut 1900 is biasedagainst the lower surface of the circular central disk portion 1809 whenthe blade 1800 and hub 1600 are secured to the output spindle 102.

Referring now to FIG. 19, the nut 1900 is seen in more detail. Thefemale threads 1901 are sized to spirally engage the male threads of theoutput spindle 102.

Referring now to FIG. 20, the individual components of FIG. 18 have beenassembled into a single unit, with the nut 1900 securing both the hub1600 and the blade 1800 to the output spindle 102. It will be noted thatthe indented lower surface 1805 provides a recess 2001 in which the nut1900 is positioned when the hub 1600 and blade 1800 are secured to theoutput spindle 102, such that a straight edge may be placed in contactwith any two segments of the metal matrix edge 703 on the lower surface2002 of the blade without encountering an intervening obstruction. Thus,the blade 1800 is enabled to cut through concrete, unimpeded by bladeattachment projections on the blade's lower surface 2002.

Referring now to FIGS. 21 and 22, a fourth embodiment hub 2100 issimilar to that of FIGS. 16 and 17, with the exception that the bladecentering shoulder 203 is replaced by a circular recess 2201.

Referring now to FIG. 23, the blade assembly 2300 also has a core 2301that, for all practical purposes, is identical to the core 1802 of FIGS.18 and 20. However, the top edge 2303 of the blade retaining nut 2302 isswedged around the central mounting hole 1808, so that the nut 2302 isintegrated into the blade assembly 2300.

Referring now to FIG. 24, the individual components of FIG. 23 have beenassembled into a single unit. It will be noted that the upper portion ofthe swedged blade retaining nut 2302 fits into the circular recess 2201within the hub 2100. It will also be noted that as with the assembly ofFIG. 20, the blade securing nut 2302 fits completely with the centralrecess 2401 of the blade assembly 2300, thereby allowing the bottomsurface 2402 of the blade assembly 2300 to cut concrete unimpeded byblade attachment projections on that surface.

Referring now to FIG. 25, it will be noted that, at the junction of afirst concrete slab 2501 and a second concrete slab 2502, there is atrip hazard 2503 that has been caused by the first slab 2501 beingraised with respect to the second slab 2502. Removal of the trip hazard,by making a dry chamfer cut on the first concrete slab 2501, will now bedescribed in detail with reference to the remaining drawing figures. Thechamfer, when complete, will have a 1:8 rise. Both slabs 2501 and 2502rest on a substrate 2504 of gravel, sand or soil. Using the right-anglegrinder motor 100 with the hub 200 and blade 700 mounted thereon, afirst chamfer cut 2505 is made on the edge of concrete slab 2501, whichhas raised with respect to the second concrete slab 2502. It will benoted that the bottom surface of the blade 901 is in close proximity tothe lower cut surface 2506. However, as heads 1003 of theblade-attachment screws 801 are flush with the lower surface of theblade 700, they are shielded from abrasive action of the concrete withinthe cut 2505. In order to protect the hub 200 from abrasion by theconcrete, the cut must stop before the rotating hub 200 contacts theupper edge 2507 of the cut concrete. Using a blade having a diameter ofabout 8 inches (about 203 mm), a 2.375 inch deep cut may be made withoutendangering the hub.

Referring now to FIG. 26, the blade has been removed from the cut 2505.It will be noted that a first cantilevered ledge 2601 extends over thecut 2505.

Referring now to FIG. 27, the cantilevered ledge 2601 has been fracturedby hitting it with a hammer or other similar instrument.

Referring now to FIG. 28, a second chamfer cut 2801 is made, which is acontinuation of the first chamfer cut 2505. Once again, in order toprotect the hub 200 from abrasion by the concrete, the cut must stopbefore the rotating hub 200 contacts the upper edge 2802 of the cutconcrete.

Referring now to FIG. 29, the blade has been removed from the cut 2801.It will be noted that a second cantilevered ledge 2901 extends over thecut 2801.

Referring now to FIG. 30, the second cantilevered ledge 2901 has beenfractured by hitting it with a hammer or other similar instrument.

Referring now to FIG. 31, a third chamber cut has been made whichremoves the remainder 3101 of the trip hazard 2503.

Referring now to FIG. 32, the first concrete slab 2501 is shown with thea completed chamfer cut 3201. The cutting equipment, which consists ofthe right-angle grinder motor 100, the attached hub 200 and blade 700,have been removed, as have been the trip hazard debris pieces 2601, 2801and 3101.

With training, a skilled worker can make an angled chamfer cut into theedge of a raised concrete slab, so that a smooth transition between alower slab and the raised slab may be formed. Trip hazards of slightlymore than 2.54 cm height can be removed in using three cuts with aneight-inch blade. Trip hazards of nearly two inches in height can beremoved with additional cuts, using the invention as heretoforedescribed.

Although only several embodiments of the apparatus and a singleembodiment of the cutting method have been heretofore described, it willbe obvious to those having ordinary skill in the art that changes andmodifications may be made thereto without departing from the scope andthe spirit of the invention as hereinafter claimed.

1. In combination with a right angled grinder motor having a threaded,rotatable output spindle and no provision for water cooling of a deviceattached to the output spindle, an apparatus for making dry chamfer cutson the edges of concrete slabs, the apparatus comprising: a hub havingan attachment collar, a blade mounting flange, and a blade centeringshoulder on a lower surface of the flange, said collar, said flange andsaid shoulder being machined as a unit, said collar having a centralmounting aperture that is threaded to spirally engage the outputspindle, said flange being equipped with multiple blade attachmentholes; a generally circular blade having metal matrix edge in whichdiamond grit is embedded, said blade having a central positioningaperture sized to fit over the blade centering shoulder, said blade alsohaving multiple countersunk holes which align with the blade attachmentholes of the flange; and multiple blade attachment screws havingcountersinking heads, said countersinking heads being flush with a lowersurface of the blade when the blade is secured to the flange with saidscrews.
 2. The combination of claim 1, wherein said blade attachmentholes are threaded to engage the blade attachment screws.
 3. Thecombination of claim 1, wherein said blade attachment holes areunthreaded, and nuts biased against an upper surface of the flange areemployed to secure an end of each screw opposite the countersinkinghead.
 4. The combination of claim 1, wherein said collar has a pair ofopposed flattened parallel sides sized to receive a wrench, with whichsaid hub may be tightened onto said threaded output spindle.
 5. Thecombination of claim 1, wherein each of said blade attachment holes insaid flange are countersunk to receive a portion of the countersinkinghead of a blade attachment screw.
 6. The combination of claim 3, whereineach of said nuts is of a self-locking type.
 7. The combination of claim1, wherein said hub is generally symmetrical about an axis of rotationpassing through the center of said mounting aperture.
 8. The combinationof claim 8, wherein the blade attachment holes in said flange areperpendicular to the axis of rotation, and evenly spaced about saidaxis.
 9. A cutting apparatus mountable on a rotatable threaded outputspindle of a right-angle grinder motor a right angled grinder motorhaving a threaded, rotatable output spindle and no provision for watercooling of the cutting apparatus, said cutting apparatus comprising: ahub having an axis of rotation and a central mounting aperturecoincident with said axis, said aperture being threaded to spirallyengage the output spindle, and thereby secure said hub to said outputspindle; a generally circular blade having an axis of rotation, a metalmatrix edge in which diamond grit is embedded, an upper major surfacewhich mates to said hub, said blade also having a plurality ofcountersunk attachment holes perpendicular to said axis of rotation; anda blade attachment screw having a countersinking head for eachattachment hole, said blade attachment screws securing said blade tosaid hub such that the head of each screw is flush with a lower surfaceof said blade.
 10. The cutting apparatus of claim 9, wherein said hubincludes a flange having multiple blade attachment holes which alignwith the countersunk attachment holes of said blade.
 11. The cuttingapparatus of claim 10, wherein said hub further includes a bladecentering shoulder on a lower surface of said flange, and said bladefurther includes a central positioning aperture sized to mate with saidshoulder in a non-interference fit.
 12. The cutting apparatus of claim10, wherein said blade attachment holes are threaded to engage the bladeattachment screws.
 13. The combination of claim 10, wherein said bladeattachment holes are unthreaded, and nuts biased against an uppersurface of the flange are employed to secure an end of each screwopposite the countersinking head.
 14. A cutting apparatus mountable on arotatable threaded output spindle of a right-angle grinder motor havingno provision for water cooling of the cutting apparatus, said cuttingapparatus comprising: a hub having an axis of rotation and a centralmounting aperture coincident with said axis, said aperture sized to fitover the output spindle, said hub having a lower blade backing surface;a generally circular blade having an axis of rotation, a generallycircular laminar metal core formed so as to have a center portion with araised upper surface and an indented lower surface, said core having aplanar flange portion extending radially from the center portion, saidflange portion having an outer circular circumferential edge, said bladehaving a metal matrix edge affixed to the circumferential edge of theflange portion, said metal matrix edge being embedded with diamond grit,said center portion having a central mounting hole sized to fit over theoutput spindle, at least a portion of said raised upper surface matingwith the lower blade backing surface of said hub; and a nut sized tospirally engage the threads of the output spindle, and thereby securethe blade and the hub to the output spindle.
 15. The cutting apparatusof claim 14, wherein said core is formed from a single piece of sheetsteel.
 16. The cutting apparatus of claim 15, wherein the center portionof said core is bell shaped, having a circular central disk portionwhich incorporates the central mounting hole, said central disk portionbeing coupled to a conical-shaped skirt portion that is, in turn,coupled to the flange portion.
 17. The cutting apparatus of claim 16,wherein the nut is biased against the circular central disk portion whenthe blade and hub are secured to the output spindle.
 18. The cuttingapparatus of claim 17, wherein the core's indented lower surfaceprovides a recess in which the nut is positioned when the hub and bladeare secured to the output spindle, such that a straight edge may beplaced in contact with any two segments of the metal matrix edge on thelower surface of the blade without encountering an interveningobstruction.
 19. The cutting apparatus of claim 16, wherein said nut isswedged within the central mounting hole.
 20. The cutting apparatus ofclaim 14, wherein the lower surface of the hub is recessed to receive atleast part of the raised center portion of the core.